Method and apparatus for allocating and signaling ack/nack resources in a wireless communication system

ABSTRACT

A method and apparatus for allocating and signaling ACK/NACK resources in a wireless communication system are provided, in which a Node B determines to use ACK/NACK resources within a predetermined fixed-size first resource group for ACK/NACK transmission for non-persistently scheduled data channels, the ACK/NACK resources being implicitly mapped to SCCHs carrying scheduling information about the non-persistently scheduled data channels, and allocates ACK/NACK resources within a predetermined flexible-size second resource group for ACK/NACK transmission for persistently scheduled data channels and transmits resource indication information explicitly indicating the allocated ACK/NACK resources to at least one UE.

PRIORITY

This application claims priority under 35 U.S.C. §119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onJan. 10, 2007 and assigned Serial No. 2007-3038, a Korean PatentApplication filed in the Korean Intellectual Property Office on Mar. 21,2007 and assigned Serial No. 2007-27626, a Korean Patent Applicationfiled in the Korean Intellectual Property Office on May 4, 2007 andassigned Serial No. 2007-43785, and a Korean Patent Application filed inthe Korean Intellectual Property Office on May 25, 2007 and assignedSerial No. 2007-51059, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a wireless communicationsystem. More particularly, the present invention relates to a method andapparatus for transmitting and receiving an Acknowledgment/NegativeAcknowledgment (ACK/NACK) for Hybrid Automatic Repeat reQuest (HARQ).

2. Description of the Related Art

There are two main error control schemes in a data transmission system,Forward Error Correction (FEC) and Automatic Repeat reQuest (ARQ). AnFEC system attempts to correct errors in received data. If the errorcorrection is successful, the correct data is decoded. If the errorcorrection has failed, the wrong data is provided to a user or the datais lost. In an ARQ system, a transmitter transmits data using an FECcode with a good error correction capability and if an error is detectedfrom the received data, a receiver requests retransmission to thetransmitter.

FEC is relatively less efficient in a good channel environment and iferror correction has failed, it decreases system reliability. On theother hand, ARQ has the advantages of high system reliability andefficient transmission with low redundancy, but it causes frequentretransmission requests in a poor channel environment, thussignificantly decreasing system efficiency. To overcome theseshortcomings, HARQ was proposed by combining FEC and ARQ in anappropriate manner.

HARQ is a scheme that attempts to correct errors in a received codeddata (a HARQ packet). It determines from a simple error detection codesuch as a Cyclic Redundancy Check (CRC) whether to requestretransmission of the HARQ packet. After determining the presence orabsence of errors in the received HARQ packet, the receiver feeds backan ACK or NACK to the transmitter. The transmitter retransmits the HARQpacket or transmits a new HARQ packet according to the ACK or NACK.

The receiver uses appropriate radio resources for the ACK/NACKtransmission. The ACK/NACK is transmitted on a few subcarriers in anOrthogonal Frequency Division Multiplexing (OFDM) wireless communicationsystem and on a predetermined code channel in a Wideband Code DivisionMultiple Access (WCDMA) system. In general, HARQ packets are transmittedsimultaneously to a plurality of users for one Transmission TimeInterval (TTI). Therefore, ACKs/NACKs are also transmittedsimultaneously for the HARQ packets.

When a Node B allocates downlink data channels to User Equipments (UEs),it also allocates control channel resources in which the UEs willtransmit ACK/NACKs for the downlink data channels. For uplink datatransmission, the Node B receives uplink packet data from the UEs onuplink data channels and then transmits ACK/NACKs for the packet data inresources agreed between the Node B and the UEs.

In general, limited resources are available to a system and the systemresources should be appropriately divided for channels including datachannels and ACK/NACK CHannels (ACKCHs). Hence, it is significant toallocate as much resources as needed for a given TTI to the ACKCHs. Todescribe the resource allocation, an Enhanced Universal TerrestrialRadio Access (EUTRA)-OFDM downlink frame structure is shown in FIG. 1,by way of example. UTRA is the future-generation mobile communicationstandards of the 3^(rd) Generation Partnership Project (3GPP).

Referring to FIG. 1, a system bandwidth 101 is 10 MHz and a total of 50Resource Blocks (RBs) 102 are defined in the system bandwidth 101. EachRB 102 includes 12 subcarriers and each 1-ms TTI 105 has 14 OFDM symbolintervals 104. One downlink data channel can be formed with one or moreRBs.

In the downlink frame structure of FIG. 1, up to 50 downlink datachannels can be scheduled at the same time for one TTI 105. Accordingly,up to 50 uplink ACKCHs are required. In real implementation, 10 or 20data channels are scheduled for one TTI on average and as many uplinkACKCHs are needed for the data channels. Since the number of availableACKCHs is very different from the average number of actually usedACKCHs, an efficient resource allocation is important.

If the Node B explicitly notifies UEs of ACKCHs established for datachannels in every TTI, only as many ACKCHs as needed can be allocatedfor the TTI. Thus, for downlink data transmission, the UEs transmitACK/NACKs in the notified ACK/NACK resources. For uplink datatransmission, the UEs detect ACK/NACKs transmitted by the Node B fromACK/NACK resources signaled by the Node B. Hence, it is significant toreduce the amount of resources for the signaling, i.e. signalingoverhead. The explicit signaling of information about ACK/NACK resourcesfrom the Node B to the UEs for each TTI results in a large signalingoverhead.

Accordingly, there exists a need for optimizing the amount of resourcesallocated to ACKCHs and the overhead of signaling the ACK/NACK resourcesin order to increase system capacity through efficient use of radioresources.

SUMMARY OF THE INVENTION

An aspect of exemplary embodiments of the present invention is toaddress at least the problems and/or disadvantages and to provide atleast the advantages described below. Accordingly, an aspect ofexemplary embodiments of the present invention is to provide a resourceallocation method and apparatus for optimizing the amount of ACK/NACKresources in a wireless communication system.

Another aspect of exemplary embodiments of the present invention is toprovide a method and apparatus for optimizing the overhead of signalinginformation about ACK/NACK resources in a wireless communication system.

A further aspect of exemplary embodiments of the present invention is toprovide a method and apparatus for signaling information about ACK/NACKresources in a different manner depending on whether data channelresources are scheduled persistently or non-persistently in a wirelesscommunication system.

In accordance with an aspect of exemplary embodiments of the presentinvention, there is provided a method for allocating and signalingACK/NACK resources in a wireless communication system, in which it isdetermined to use ACK/NACK resources within a predetermined fixed-sizefirst resource group for ACK/NACK transmission for non-persistentlyscheduled data channels, the ACK/NACK resources being implicitly mappedto Scheduling Control CHannels (SCCHs) carrying scheduling informationabout the non-persistently scheduled data channels, and ACK/NACKresources within a predetermined flexible-size second resource group areallocated for ACK/NACK transmission for persistently scheduled datachannels and resource indication information explicitly indicating theallocated ACK/NACK resources is transmitted to at least one UE.

In accordance with another aspect of exemplary embodiments of thepresent invention, there is provided an apparatus of a Node B forallocating and signaling ACK/NACK resources in a wireless communicationsystem, in which a controller determines to use ACK/NACK resourceswithin a predetermined fixed-size first resource group for ACK/NACKtransmission for non-persistently scheduled data channels, the ACK/NACKresources being implicitly mapped to SCCHs carrying schedulinginformation about the non-persistently scheduled data channels, anddetermines to allocate ACK/NACK resources within a predeterminedflexible-size second resource group for ACK/NACK transmission forpersistently scheduled data channels, and a generator generates andtransmits resource indication information explicitly indicating theallocated ACK/NACK resources to at least one UE.

In accordance with a further aspect of exemplary embodiments of thepresent invention, there is provided a method for receiving ACK/NACKresources in a wireless communication system, in which it is determinedto use ACK/NACK resources within a predetermined fixed-size firstresource group for ACK/NACK transmission for a non-persistentlyscheduled data channel, the ACK/NACK resources being implicitly mappedto an SCCH carrying scheduling information about the non-persistentlyscheduled data channel, if the non-persistently scheduled data channelis allocated to a UE, and resource indication information explicitlyindicating allocated ACK/NACK resources for an ACKCH corresponding to apersistently scheduled data channel within a predetermined flexible-sizesecond resource group is received, if the persistently scheduled datachannel is allocated to the UE.

In accordance with still another aspect of exemplary embodiments of thepresent invention, there is provided an apparatus of a UE for receivingACK/NACK resources in a wireless communication system, in which acontroller determines to use ACK/NACK resources within a predeterminedfixed-size first resource group for ACK/NACK transmission for anon-persistently scheduled data channel, the ACK/NACK resources beingimplicitly mapped to an SCCH carrying scheduling information about thenon-persistently scheduled data channel, if the non-persistentlyscheduled data channel is allocated to the UE, and determines to receiveresource indication information explicitly indicating allocated ACK/NACKresources for an ACKCH corresponding to a persistently scheduled datachannel within a predetermined flexible-size second resource group, ifthe persistently scheduled data channel is allocated to the UE, and areceiver receives the resource indication information under control ofthe controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates an exemplary downlink resource structure

FIG. 2 illustrates an ACK/NACK resource allocation scheme according tothe present invention;

FIG. 3 illustrates scheduling physical channel formats according to thepresent invention;

FIG. 4 illustrates another ACK/NACK resource allocation scheme accordingto the present invention;

FIG. 5 illustrates an exemplary ACK/NACK resource allocation accordingto the present invention;

FIG. 6 is a flowchart of an operation of a Node B according to thepresent invention;

FIG. 7A is a flowchart of an operation of a UE according to the presentinvention;

FIG. 7B is a flowchart of an operation of the UE during HARQtransmission in the case of persistent scheduling according to thepresent invention;

FIG. 8 is a block diagram of a Node B apparatus according to the presentinvention;

FIG. 9 is a block diagram of a UE apparatus according to the presentinvention;

FIG. 10 illustrates an ACK/NACK resource allocation scheme in a MultipleInput Multiple Output (MIMO) system according to another embodiment ofthe present invention;

FIG. 11 illustrates an ACK/NACK resource allocation scheme consideringcell coverage according to a third embodiment of the present invention;and

FIG. 12 illustrates an ACK/NACK resource allocation scheme according toa fourth embodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed constructionand elements are provided to assist in a comprehensive understanding ofexemplary embodiments of the invention. Accordingly, those of ordinaryskill in the art will recognize that various changes and modificationsof the embodiments described herein can be made without departing fromthe scope and spirit of the invention. Also, descriptions of well-knownfunctions and constructions are omitted for clarity and conciseness.

While exemplary embodiments of the present invention will be describedin the context of an OFDM cellular wireless communication system,particularly an EUTRA system based on 3GPP Universal MobileTelecommunication Services (UMTS), it is to be clearly understood bythose skilled in the art that the subject matter of the presentinvention is also applicable to other communication systems havingsimilar technological backgrounds and channel structures with slightmodifications within the scope and spirit of the present invention.

The present invention pertains to efficient allocation and signaling ofchannel resources in a wireless communication system. In accordance withthe present invention, a different signaling scheme is used for ACK/NACKresource allocation depending on the scheduling type of data channels.Data channels can be scheduled in two ways according to thecharacteristics of data traffic.

For irregular data transmission such as Internet browsing or when usinga gaming service, a Node B selects appropriate radio resources and anappropriate TTI for the data transmission, each time data is generated.When transmitting the data, the Node B signals scheduling informationindicating the selection result to a UE on a Scheduling Control CHannel(SCCH). This scheduling type is called non-persistent scheduling.

For almost real-time or regular data traffic such as Voice over InternetProtocol (VoIP), the Node B does not need to select resources for thedata transmission in every TTI and notify the UE of the selectedresources. Hence, scheduling information about the resource allocationfor the data traffic is signaled once at an initial scheduling and isvalid for the subsequent data transmissions. The validity of thescheduling information lasts persistently or for a predetermined time.This scheduling type in which scheduling information is valid for aplurality of TTIs or for a plurality of data packets is calledpersistent scheduling.

Depending on the persistent or non-persistent scheduling type for datatransmission, ACK/NACK resources are allocated and signaled in adifferent manner in the present invention. More specifically, fornon-persistently scheduled data transmission, ACK/NACK resources areindicated by the index of an SCCH. For persistently scheduled datatransmission, ACK/NACK resources are explicitly notified during aninitial scheduling and are still valid afterwards. Since ACK/NACKresource allocation depends on the data scheduling type, the useefficiency of the entire resources is increased and the signalingoverhead of the ACK/NACK resources is decreased.

In a MIMO scheme in which a plurality of codewords can be transmittedsimultaneously through a plurality of transmit/receive antennas on asingle data channel, two or more ACKCHs are needed for the codewords. Inthis context, the present invention provides a method for allocatingACK/NACK resources and signaling the allocated ACK/NACK resources, whichsuits for MIMO transmission.

As used herein, the term “ACK/NACK resources” is defined as resourcesallocated for an ACKCH.

Embodiment 1

FIG. 2 illustrates an ACK/NACK resource allocation scheme according tothe present invention.

Referring to FIG. 2, a Node B scheduler 200 selects non-persistentscheduling 211 or persistent scheduling 212 for data channels.

In the non-persistent scheduling 211, M SCCHs 203 deliver schedulinginformation about M data channels. Each SCCH is a physical layer controlchannel carrying scheduling information about one data channel. ACK/NACKresources in which an ACK/NACK is transmitted for a data channel areimplicitly indicated by the index of an SCCH 203 mapped to the datachannel. Hence, different data channels, that is, different SCCHs 203are one-to-one mapped to ACKCHs 207 within a fixed-size resource group209, as indicated by reference numeral 205.

The simplest mapping rule is that SCCH #n is mapped to ACKCH #n,although other mapping rules are also available. This mapping betweenthe SCCHs 203 and the ACKCHs 207 obviates the need for the Node B'sexplicit signaling of the indexes of the ACKCHs 207 to UEs, therebyreducing signaling overhead.

Meanwhile, in order to define SCCHs of various formats and sizes,Control Channel Elements (CCEs) each having a predetermined number ofsubcarriers are defined and labeled with CCE indexes. An SCCH can beformed with one or more CCEs. Then, the index of a CCE (or CCEs) formingan SCCH is mapped to ACK/NACK resources, instead of the index of theSCCH. Thus a UE can find out the index of an allocated ACKCH from theindex of the CCE forming the SCCH without separate signaling of theindex of the ACKCH. In this manner, ACK/NACK resources fornon-persistently scheduled data are implicitly signaled by the indexesof CCEs, instead of the indexes of the SCCHs 203. If an SCCH includes aplurality of CCEs, one of the CCE indexes, for example, the lowest CCEindex can be mapped to ACK/NACK resources.

The illustrated case of FIG. 2 is based on the assumption that up to Mdata channels can be scheduled for one TTI. The number of scheduled datachannels for each TTI may vary according to a decision of the Node Bscheduler 200, which in turn may change the numbers of the SCCHs 203 andthe ACKCHs 207. For the non-persistent scheduling 211, the resourcegroup 209 is preset for as many or more ACKCHs for a maximum allowednumber of data channels to thereby enable rapid allocation of ACK/NACKresources without explicit signaling.

In the persistent scheduling 212, once resources are scheduled for datachannels using SCCHs 204 at an initial data transmission, schedulinginformation about the resources is valid persistently or for apredetermined number of following TTIs, without transmission of newscheduling information.

However, considering the number of persistently scheduled UEs isdifferent in each cell and the number of persistently scheduled datachannels is also different in each TTI, the Node B explicitly transmitsto UEs resource indication information indicating ACKCHs 208 within aflexible-size resource group 210 in the persistent scheduling 212, asindicated by reference numeral 206. The resource indication informationis still valid to the UEs afterwards as long as the same resourceallocation is maintained for data.

When needed, for example, to gather ACK/NACK resources scattered acrossRBs, it is possible to reallocate ACK/NACK resources for a persistentlyscheduled data channel by additional signaling during a service. TheACK/NACK resource reallocation can be indicated by high-layer signalinginformation transmitted on a persistently scheduled data channel. A UEacquires ACK/NACK resource indication information from the high-layersignaling information and transmits an ACK/NACK for a data channelreceived later in the resources indicated by the ACK/NACK resourceindication information.

As illustrated in FIG. 2, the ACK/NACK resource indication informationfor the persistently scheduled data channels is signaled by Layer 1(L1)/Layer 2 (L2) on control channels or by high-layer protocolinformation, as indicated by reference numeral 206. Even when persistentscheduling information about the data channels is transmitted by L1/L2signaling, the ACK/NACK resource indication information can betransmitted by high-layer signaling. Since transmission of initialscheduling information suffices in the persistent scheduling 212,explicit signaling of ACK/NACK indication information does not cause agreat increase in signaling overhead even though as much ACK/NACKresources as needed are allocated for each TTI.

In the persistent scheduling 212, data is transmitted in persistentlyscheduled resources during an Initial HARQ transmission. If theinitially transmitted data has errors, the Node B can explicitlyschedule data channel resources for an HARQ retransmission. Hence, anACK/NACK is transmitted for the retransmitted data on an ACKCH 207within the fixed-size resource group 209, implicitly mapped to the indexof an SCCH 203 that schedules a data channel during the HARQretransmission. Alternatively, the ACK/NACK can be transmitted on thesame or a different ACKCH from a previous persistently scheduled ACKCHin the flexible-size resource group 210. Therefore, the ACK/NACKresources used for the Initial HARQ transmission can be utilized forother channels.

For example, in the case where an ACK/NACK is transmitted on an ACKCH207 mapped to the index of an SCCH that schedules data resources or theindex of a CCE forming the SCCH during an HARQ retransmission, ACK/NACKresources allocated for a persistently scheduled data channel for a UEare confined to an Initial HARQ transmission only. Since the Node B canallocate the ACK/NACK resources allocated for the initial HARQtransmission to ACKCHs of other UEs or other channels of the UE,resource use efficiency is improved. In other words, ACK/NACK resourcesallocated persistently by persistent data scheduling are valid only forthe Initial HARQ transmission and the ACK/NACK resources implicitlyindicated by the SCCH are used for ACK/NACK transmission during the HARQretransmission.

The above-described ACK/NACK resource allocation applies to both thedownlink and the uplink. For downlink data transmission, the SCCHs 203and 204 carry resource allocation information about downlink data fromthe Node B to the UEs and the ACKCHs 207 and 208 deliver ACKs/NACKs forthe downlink data from the UEs to the Node B. For uplink datatransmission, the SCCHs 203 and 204 deliver resource allocationinformation about uplink data that the UEs will transmit to the Node Band the ACKCHs 207 and 208 carry ACK/NACKs for the uplink data from theNode B to the UEs.

FIG. 3 is an exemplary downlink scheduling physical channel formataccording to the present invention, when persistent schedulinginformation is transmitted by L1/L2 signaling like non-persistentscheduling information. Reference numeral 300 denotes the informationformat of a non-persistent SCCH and reference numeral 301 denotes theinformation format of a persistent SCCH.

Referring to FIG. 3, a UE receives and decodes a first part 303 (Part 1)of an SCCH and determines, based on a scheduling type indicator 302,whether the SCCH is for non-persistent scheduling or persistentscheduling. The UE acquires scheduling information 305 or 306 byreceiving and decoding a second part 304 (Part 2) according to thescheduling type indicator 302. The scheduling information 305 or 306includes resource indication information indicating resources allocatedfor a data channel, the Modulation and Coding Scheme (MCS) level of thedata channel, HARQ information, and MIMO information.

Compared to the non-persistent scheduling information 305, thepersistent scheduling information 306 further includes ACK/NACK resourceindication information and scheduling duration information indicating aduration for which the persistent scheduling information 306 is valid.It can be further contemplated that the non-persistent SCCH format 300is identical to the persistent SCCH format 301 and the schedulingduration information and the ACK/NACK indication information aretransmitted separately by L1/L2 signaling or high-layer signaling.

When an initial transmission is scheduled through persistent schedulingand signaled by L1/L2 signaling, ACK/NACK resources can be implicitlyindicated by an SCCH as in non-persistent scheduling. ACK/NACK resourcescan be explicitly signaled in a persistently scheduled initial datatransmission or the following data transmission that is not indicated byan SCCH, ACK/NACK resources can be explicitly signaled. For example, ifpersistent scheduling information is signaled to a UE on SCCH #k, the UEreceives data in data channel resources indicated by SCCH #k andtransmits an ACK/NACK on ACKCH #k mapped to SCCH #k for the receiveddata. For the following data received in the data channel resources, theUE transmits ACK/NACKs for the data in ACK/NACK resources explicitlyindicated by high-layer signaling information included in the datainitially received in the data channel resources.

The above ACKCH use example applies to high-layer signaling ofpersistent scheduling information about a data channel. Since a datachannel carrying initial data including the persistent schedulinginformation as high-layer signaling information is scheduled for a UE byan SCCH, the UE transmits an ACK/NACK in ACK/NACK resources mapped tothe SCCH or a CCE forming the SCCH. After successful reception of theinitial data, the UE transmits an ACK/NACK in ACK/NACK resourcesindicated by the high-layer signaling information included in theinitial data.

FIG. 4 illustrates another ACK/NACK resource allocation scheme accordingto the present invention.

Referring to FIG. 4, ACKCHs 403 for persistently scheduled data channelsshare a resource group 405 with CQICHs 404. UEs transmit statusinformation about downlink channels to the Node B on the CQICHs 404. TheNode B explicitly indicates a transmission timing and resources for aCQICH to each UE, as indicated by reference numeral 401. Like the ACKCHs403, the number of the CQICHs 404 may vary for each cell or for eachTTI. The CQICHs 404 and the ACKCHs 403 share the flexible-size resourcegroup 405 and the Node B controls resources allocated to the ACKCHs 403and the CQICHs 404 within the resource group 405 by shifting a resourceboundary 402 according to situations. Hence, the entire resources areefficiently used.

FIG. 5 illustrates an exemplary ACK/NACK resource allocation accordingto the present invention. The ACK/NACK resource allocation is performedin compliance with the EUTRA uplink SC-FDMA standards of the 3GPP, byway of example.

Referring to FIG. 5, a transmission bandwidth 500 of 10 MHz is dividedinto 50 Resource Units (RUs) 501 to 504, each RU having 12 subcarriers.ACKCHs and CQICHs are multiplexed by Code Division Multiplexing (CDM) ina first RU 501 (RU #1), a 49^(th) RU 503 (RU #49), and a 50^(th) RU 504(RU #50) by applying different sequences or different cyclically shiftedsequences of the same sequence to the ACKCHs and the CQICHs. Datachannels are multiplexed with the ACKCHs and the CQICHs by FrequencyDivision Multiplexing (FDM) in the 2^(nd) to 48^(th) RUs 502 (RU #2 toRU #48).

M ACKCHs, ACKCH #1 to ACKCH #M, for non-persistently scheduled datachannels are transmitted in RU #1 by CDM and the remaining CDM resourcesof RU #1 are allocated to ACKCH #(M+1) to ACKCH #12 for persistentlyscheduled data channels. In addition to ACKCH #(M+1) to ACKCH #12, RU#49 and RU #50 are used as ACK/NACK resources for persistently scheduleddata channels. In a TTI with a small number of persistently scheduleddata channels, RU #49 and RU #50 are used for data channels along withthe data channels 505 of RU #2 to RU #48, or they are dedicated toCQICHs.

While RU #49 is allocated to 1^(st) to K^(th) CQICHs 509 to 510 (CQICH#1 to CQICH #K) in FIG. 5, there is no need for drawing a boundary in RU#49 and CQICHs can also be allocated in RU #50. Since the amount andindexes of ACK/NACK resources and CQICH resources are controlled on aTTI basis, as much radio resources as needed can be efficiently used.

Instead of signaling absolute values such as a cyclic shift value of aCDM sequence, an additional orthogonal sequence index, and a transmittedRU index to a UE as resource indication information about a CQICH and anACKCH for a persistently scheduled data channel in the flexible-sizeresource group 405, an offset from the boundary of the fixed-size ACKCHresource group can be signaled to the UE. When each uplink channel indexis defined by a combination of a cyclic shift value of a CDM sequence,an orthogonal sequence index, and a transmitted RU index as illustratedin FIG. 5, the offset refers to a relative index with respect to ACKCH#M at the boundary of the fixed-size ACKCH resource group. For instance,ACKCH #(M+m) is indicated by an offset m.

FIG. 6 is a flowchart of an operation of the Node B according to thepresent invention.

Referring to FIG. 6, the Node B prepares to schedule a downlink and/oruplink data channel and an ACKCH for a UE in step 600. Specifically, theNode B collects information required for scheduling, such as ascheduling type for data traffic, buffer status, and resource status. Instep 601, the Node B determines a scheduling type for the data channeland a transport format for the data channel such as allocated resourcesand an MCS level, and then formats scheduling information according tothe determination result.

In step 602, the Node B determines whether the scheduling type ispersistent or non-persistent. In the case of the persistent scheduling,the Node B determines ACK/NACK resources and formats ACK/NACK resourceindication information to notify the UE of the ACK/NACK resources instep 603. The scheduling type is determined according to the trafficcharacteristics of the data channel. In step 604, the Node B transmitsthe scheduling information of the data channel and the ACK/NACK resourceindication information to the UE by L1/L2 signaling or high-layersignaling.

In the case of the non-persistent scheduling, ACK/NACK resources aredetermined according to the index of an SCCH mapped to the data channel.Therefore, the Node B transmits only the scheduling information of thedata channel on an SCCH having an SCCH index to the UE in step 605.

FIG. 7A is a flowchart of an operation of the UE according to thepresent invention.

Referring to FIG. 7A, the UE acquires scheduling information by decodingan SCCH in every scheduling interval (e.g. in every TTI) in step 700 anddetermines whether there are data channel resources allocated to the UEin the current scheduling interval, that is, determines from thescheduling information whether the UE has been scheduled in the currentscheduling interval in step 701. If the UE has not been scheduled, theUE returns to step 700. If the UE has been scheduled, it transmitsscheduled data according to the scheduling information if uplink datatransmission is scheduled or receives and decodes scheduled dataaccording to the scheduling information if downlink data reception isscheduled.

In step 703, the UE determines whether the scheduling type of data usedin FIG. 702 is persistent or non-persistent. The UE can determine thescheduling type from the scheduling type indicator of the schedulinginformation or the traffic characteristics of the data channel. In thecase of the persistent scheduling type, the UE detects ACK/NACKresources explicitly indicated when the data is initially scheduled bypersistent scheduling in step 704 and transmits an ACK/NACK to the NodeB in the ACKCH resources if the downlink data reception is scheduled orreceives an ACK/NACK in the ACKCH resources from the Node B if theuplink data transmission is scheduled in step 706.

In the case of the non-persistent scheduling type, the UE detectsACK/NACK resources implicitly mapped to the SCCH corresponding to thenon-persistently scheduled data channel in step 705 and transmits orreceives an ACK/NACK to or from the Node B in the ACK/NACK resources instep 706.

FIG. 7B is a flowchart of an operation of the UE when it transmits anACK/NACK on the uplink for a persistently scheduled downlink datachannel according to the present invention.

Referring to FIG. 7B, the UE receives persistent scheduling informationthat persistently schedules resources for a downlink data channel and anuplink ACKCH by L1/L2 signaling or high-layer signaling in step 711.That is, the persistent scheduling information includes ACK/NACKresource indication information for the uplink ACKCH. In step 712, theUE receives a data packet periodically on the persistently scheduleddata channel according to the persistent scheduling information.

In step 713, the UE determines whether the data packet is an initialHARQ transmission packet or an HARQ retransmission packet. In the caseof the initial HARQ transmission, the UE proceeds to step 715 and in thecase of the HARQ retransmission, the UE goes to step 714. In step 715,the UE transmits an ACK/NACK for the data packet in the ACK/NACKresources explicitly indicated in step 701. In step 714, the UEdetermines whether the persistent scheduling information has beenreceived together with the data packet. If they have been receivedseparately, the UE transmits an ACK/NACK for the data packet in theACK/NACK resources explicitly indicated in step 701 in step 715. If theyhave been received together, the UE transmits an ACK/NACK on an ACKCHmapped to the SCCH or a CCE of the SCCH in step 716.

FIG. 8 is a block diagram of an apparatus of the Node B according to thepresent invention.

Referring to FIG. 8, a data channel scheduler 800 determines radioresources and MCS levels for data by scheduling data channels. Ascheduling information generator 803 generates scheduling informationrepresenting the determination results of the data channel scheduler 800and a control channel generator 805 channel-encodes the schedulinginformation and transmits it on an SCCH. The scheduling information canbe transmitted by L1/L2 signaling or high-layer signaling.

A controller 801 determines to use ACK/NACK resources implicitly mappedto SCCHs for non-persistently scheduled data channels. For persistentlyscheduled data channels, the controller 801 determines that ACK/NACKresources need to be allocated within a flexible-size resource group.The controller 801 notifies an ACKCH scheduler 802 of the determination.

The ACKCH scheduler 802 determines resource allocation for ACKCHs forthe data channels. It does not schedule ACKCHs for the non-persistentlyscheduled data channels and allocates only resources for ACKCHs in theflexible-size resource group for the persistently scheduled datachannels, under the control of the controller 801. An indicationinformation generator 804 generates ACK/NACK resource indicationinformation explicitly indicating the determination of the ACKCHscheduler 802. The control channel generator 805 channel-encodes theACK/NACK resource indication information and transmits it by L1/L2scheduling or high-layer scheduling.

FIG. 9 is a block diagram of a receiver of the UE according to thepresent invention.

Referring to FIG. 9, an SCCH decoder 900 detects an SCCH signal mappedto SCCH resources from a received (RX) signal 906 and acquiresscheduling information by decoding the SCCH signal. When the decoding ofthe scheduling information is successful, a controller 901 determineswhether the scheduling information indicates a persistent ornon-persistent scheduling type. In the case of the persistent schedulingtype, the controller 901 controls a Multiplexer (MUX) 902 according toan ACK/NACK resource signaling scheme to provide a signaling signalindicating ACK/NACK resources in the received signal to an indicationinformation decoder 903. If the ACK/NACK resource signaling signal isincluded in the scheduling information, the MUX 902 selects thescheduling information and provides it to the indication informationdecoder 903.

The indication information decoder 903 acquires the ACK/NACK resourceindication information by decoding the signaling signal included in thescheduling information. During downlink data reception, the ACK/NACKresource indication information is used for an ACK/NACK generator andmapper 904 to generate an ACK/NACK for downlink data and map theACK/NACK to ACK/NACK resources. For uplink data transmission, theACK/NACK resource indication information is used for an ACK/NACKdetector 905 to detect an ACK/NACK mapped to the ACK/NACK resources fromthe RX signal 906.

In the case of the non-persistent scheduling, the controller 901 detectsACK/NACK resources implicitly mapped to the SCCH indicating resourcesfor the non-persistently data channel and notifies the ACK/NACKgenerator and mapper 904 of the ACK/NACK resources for use in ACK/NACKtransmission or reception.

Embodiment 2

FIG. 10 illustrates an ACK/NACK resource allocation scheme for a MIMOsystem according to another embodiment of the present invention.

MIMO schemes are categorized into Single CodeWord MIMO (SCW-MIMO) andMulti-CodeWord MIMO (MCW-MIMO). In MCW-MIMO in which a transmittertransmits a plurality of codewords simultaneously, decoding is performedfor each codeword. Hence, as many ACKCHs as the transmitted codewordsare needed. As illustrated in FIG. 10, therefore, an ACKCH for at leastone (e.g. the first codeword) of codewords on an MCW-MIMO data channelthat is non-persistently scheduled uses ACK/NACK resources mapped to theindex of an SCCH for the first codeword, as indicated by referencenumeral 1000, whereas ACK/NACK resources for the remaining codewords areexplicitly signaled along with SCCHs 1002 for the non-persistentlyscheduled MCW-MIMO data channels, as indicated by reference numeral1003. The ACK/NACK resources share a flexible-size resource group 1005with ACKCHs for persistently scheduled data channels.

That is, for non-persistent scheduling of MCW-MIMO data, the Node Ballocates part of the flexible-size ACK/NACK resources 1005 forcodewords to which ACK/NACK resources have not been allocated, takinginto account the allocation status of the ACK/NACK resources 1005 on aTTI basis, as indicated by reference numeral 1003. The sharing of theresource group 1005 between ACKCHs for non-persistently scheduledMCW-MIMO data channels and ACKCHs for persistently scheduled MCW-MIMOdata channels leads to efficient use of radio resources.

For non-MIMO and SCW-MIMO data channels, ACK/NACK resources implicitlysignaled by the indexes of SCCHs 1001 are used as indicated by referencenumeral 1006, as described before. Therefore, ACKs/NACKs for thenon-MIMO and SCW-MIMO data channels are transmitted on ACKCHs within afixed-size resource group 1004.

Embodiment 3

FIG. 11 illustrates an ACK/NACK resource allocation scheme according toa third embodiment of the present invention. ACK/NACK resources areallocated, taking into account of the cell coverage of ACKCHs. Herein,the 3GPP EUTRA standards are considered, in which a 1-ms TTI is defined.

The cell coverage of an ACKCH is defined as a cell radius in which theACKCH is stably detected. To expand cell coverage for a limited maximumtransmit power, it is necessary to increase the reception energy of anACKCH at a receiver by increasing the transmission duration of theACKCH. However, as the transmission duration of the ACKCH increases, theamount of resources that the ACKCH occupies increases proportionally.

Therefore, for efficient use of radio resources, a flexible-sizeresource group 1101 for persistently scheduled data channels is dividedinto a first resource group 1107 having a transmission duration of 1 msand a second resource group 1108 having a transmission duration of 0.5ms. ACKCH #2.x with the 0.5-ms transmission duration 1105 or ACKCH #1.xwith the 1-ms transmission duration 1104 is allocated to a UE that issubject to persistent scheduling. The transmission duration of theallocated ACKCH is indicated by ACK/NACK resource indicationinformation, or preset between the system and the UE according to theposition of ACK/NACK resources or the index of the ACKCH.

For a UE near to the Node B, which has sufficient transmit power, theNode B instructs the UE to transmit an ACK/NACK for 0.5 ms with highpower by allocating ACKCH #2.x within the second resource group 1108,thus reducing ACK/NACK resource overhead. For a UE at a cell boundary,which does not have sufficient transmit power, the Node B increases thereception energy of an ACKCH by allocating ACKCH #1.x within the firstresource group 1107 to the UE, thus increasing ACK/NACK detectionprobability. The Node B can determine whether the UE is near or at thecell boundary by a channel status reported by the UE, the signalstrength of a signal received form the UE, or the geographical locationof the UE.

A boundary 1106 between the first and second resource groups 1107 and1108 is variable for each cell and for each TTI. The ACKCHs of thesecond resource group 1108 are not always transmitted continuously for0.5 ms. For example, ACKCH #2.1 and ACKCH #2.2 are transmittedalternately during non-successive two 2.5-ms durations and frequencyhopping can take place during the next 0.5-ms period. For example, ACKCH#1 is transmitted during non-successive time periods between 0 and 0.25ms and between 0.5 and 0.75 ms and ACKCH #2 is transmitted duringnon-successive time periods between 0.25 and 0.5 ms and between 0.75 and1 ms. For the first 0.5-ms period, ACKCH #1 and ACKCH #2 are transmittedin first frequency resources (e.g. RU #1) and for the next 0.5-msperiod, they are hopped to second frequency resources (e.g. RU #50). Inthis case, the total transmission duration of ACKCH #2.x is 0.5 ms, butsince the transmission is non-successive and frequency-hopped, time andfrequency diversities are achieved. The flexible-size ACK/NACK resources1101 can be shared between CQICHs and ACKCHs for MCW-MIMO data channelsas well as ACKCHs for persistently scheduled data.

On the other hand, since ACKCHs for non-persistently scheduled datachannels are dynamically allocated according to the indexes of SCCHs inevery TTI, the ACKCHs of a fixed-size resource group 1100 have commonlya 1-ms transmission duration 1103 to prevent a cell coverage problem.The ACKCHs of the fixed-size resource group 1100 can be multiplexed in acode or frequency domain 1102.

Embodiment 4

FIG. 12 illustrates an ACK/NACK resource allocation scheme according toa fourth embodiment of the present invention.

Referring to FIG. 12, ACKs/NACKs for non-persistently scheduled datachannels use ACK/NACK resources of a fixed-size resource group 1202mapped to SCCHs for the data channels, as in the first exemplaryembodiment of the present invention. ACK/NACK resources can be mapped toat least one CCE forming an SCCH, instead of the SCCH. In this case, anACKCH for a data channel indicated by the SCCH uses resourcescorresponding to at least one of the CCEs forming the SCCH and the UEimplicitly finds out the ACK/NACK resources by the CCE index.

As compared to the first embodiment of the present invention, the fourthembodiment of the present invention is characterized in that resourcesof the fixed-size resource group 1202 as well as those of aflexible-size resource group 1205 are available to at least one ofACKCHs for persistently scheduled data channels, CQICHs, and otherchannels.

For example, when a small number of SCCHs are used due to a small numberof active UEs in a cell or a small number of scheduled UEs for a TTI,much resources remain except for ACK/NACK resources mapped to used SCCHsin the fixed-size resource group 1202. In this case, the Node Ballocates the remaining resources and the flexible-size resource group1205 to UEs by explicit indication 1204, so that the remaining resourcesare used for transmission of at least one of ACKCHs for persistentlyscheduled data channels, CQICHs, and other channels. The UEs use theremaining resources for ACKCHs for persistently scheduled data channels,CQICHs, and other channels.

As is apparent from the above description, the present inventionincreases resource use efficiency and reduces signaling overhead byapplying an appropriate ACK/NACK resource allocation and signalingscheme according to a non-persistent scheduling type or a persistentscheduling type for data. The resulting increase in resources availablefor transmission increases system capacity.

While the invention has been shown and described with reference tocertain exemplary embodiments of the present invention thereof, it willbe understood by those skilled in the art that various changes in formand details may be made therein without departing from the spirit andscope of the present invention as defined by the appended claims andtheir equivalents.

1. A method for allocating and signaling ACKnowledgment/NegativeACKnowledgment (ACK/NACK) resources in a wireless communication system,comprising: determining to use ACK/NACK resources within a predeterminedfixed-size first resource group for ACK/NACK transmission fornon-persistently scheduled data channels, the ACK/NACK resources beingimplicitly mapped to Scheduling Control CHannels (SCCHs) carryingscheduling information about the non-persistently scheduled datachannels; and allocating ACK/NACK resources within a predeterminedflexible-size second resource group for ACK/NACK transmission forpersistently scheduled data channels and transmitting resourceindication information explicitly indicating the allocated ACK/NACKresources to at least one User Equipment (UE).
 2. The method of claim 1,wherein ACK/NACKs for initial transmission data on the persistentlyscheduled data channels are transmitted in the ACK/NACK resourcesexplicitly indicated by the resource indication information, andACK/NACKs for retransmission data associated with the initialtransmission data are transmitted in ACK/NACK resources implicitlymapped to SCCHs carrying scheduling information about the persistentlyscheduled data channels.
 3. The method of claim 1, wherein the secondresource group is shared between ACK/NACK CHannels (ACKCHs) for thepersistently scheduled data channels and Channel Quality IndicatorCHannels (CQICHs) carrying CQIs representing status information aboutdownlink radio channels.
 4. The method of claim 1, wherein an ACK/NACKfor a first data channel among the non-persistently scheduled datachannels is transmitted in ACK/NACK resources implicitly mapped to anSCCH corresponding to the first data channel in the first resourcegroup, the first channel carrying a first codeword among a plurality ofcodewords for Multi-CodeWord-Multiple Input Multiple Output (MCW-MIMO),and ACK/NACKs for second data channels carrying remaining codewords aretransmitted in explicitly signaled ACK/NACK resources in the secondresource group.
 5. The method of claim 1, wherein each ACKCHcorresponding to the non-persistently scheduled data channels has arelatively long first transmission duration, and each ACKCHcorresponding to the persistently scheduled data channels has one of thefirst transmission duration and a relatively short second transmissionduration.
 6. The method of claim 1, wherein remaining resources that arenot allocated as ACK/NACK resources for the non-persistently scheduleddata channels are allocated for transmission of at least one ACKCH forthe persistently scheduled data channels, CQICHs, and predeterminedother channels and explicitly signaled.
 7. An apparatus of a Node B forallocating and signaling ACKnowledgment/Negative ACKnowledgment(ACK/NACK) resources in a wireless communication system, comprising: acontroller for determining to use ACK/NACK resources within apredetermined fixed-size first resource group for ACK/NACK transmissionfor non-persistently scheduled data channels, the ACK/NACK resourcesbeing implicitly mapped to Scheduling Control CHannels (SCCHs) carryingscheduling information about the non-persistently scheduled datachannels, and determining to allocate ACK/NACK resources within apredetermined flexible-size second resource group for ACK/NACKtransmission for persistently scheduled data channels; and a generatorfor generating and transmitting resource indication informationexplicitly indicating the allocated ACK/NACK resources to at least oneUser Equipment (UE).
 8. The apparatus of claim 7, wherein ACK/NACKs forinitial transmission data on the persistently scheduled data channelsare transmitted in the ACK/NACK resources explicitly indicated by theresource indication information, and ACK/NACKs for retransmission dataassociated with the initial transmission data are transmitted inACK/NACK resources implicitly mapped to SCCHs carrying schedulinginformation about the persistently scheduled data channels.
 9. Theapparatus of claim 7, wherein the second resource group is sharedbetween ACK/NACK CHannels (ACKCHs) for the persistently scheduled datachannels and Channel Quality Indicator CHannels (CQICHs) carrying CQIsrepresenting status information about downlink radio channels.
 10. Theapparatus of claim 7, wherein an ACK/NACK for a first data channel amongthe non-persistently scheduled data channels is transmitted in ACK/NACKresources implicitly mapped to an SCCH corresponding to the first datachannel in the first resource group, the first channel carrying a firstcodeword among a plurality of codewords for Multi-CodeWord-MultipleInput Multiple Output (MCW-MIMO), and ACK/NACKs for second data channelscarrying remaining codewords are transmitted in explicitly signaledACK/NACK resources in the second resource group.
 11. The apparatus ofclaim 7, wherein each ACKCH corresponding to the non-persistentlyscheduled data channels has a relatively long first transmissionduration, and each ACKCH corresponding to the persistently scheduleddata channels has one of the first transmission duration and arelatively short second transmission duration.
 12. The apparatus ofclaim 7, wherein remaining resources that are not allocated as ACK/NACKresources for the non-persistently scheduled data channels are allocatedfor transmission of at least one ACKCH for the persistently scheduleddata channels, CQICHs, and predetermined other channels and explicitlysignaled.
 13. A method for receiving ACKnowledgment/NegativeACKnowledgment (ACK/NACK) resources in a wireless communication system,comprising: determining to use ACK/NACK resources within a predeterminedfixed-size first resource group for ACK/NACK transmission for anon-persistently scheduled data channel, the ACK/NACK resources beingimplicitly mapped to a Scheduling Control CHannel (SCCH) carryingscheduling information about the non-persistently scheduled datachannel, if the non-persistently scheduled data channel is allocated toa User Equipment (UE); and receiving resource indication informationexplicitly indicating allocated ACK/NACK resources for an ACK/NACKCHannel (ACKCH) corresponding to a persistently scheduled data channelwithin a predetermined flexible-size second resource group, if thepersistently scheduled data channel is allocated to the UE.
 14. Themethod of claim 13, wherein an ACK/NACK for initial transmission data onthe persistently scheduled data channel is transmitted in the ACK/NACKresources explicitly indicated by the resource indication information,and an ACK/NACK for retransmission data associated with the initialtransmission data is transmitted in ACK/NACK resources implicitly mappedto an SCCH carrying scheduling information about the persistentlyscheduled data channel.
 15. The method of claim 13, wherein the secondresource group is shared between ACKCHs for persistently scheduled datachannels and Channel Quality Indicator CHannels (CQICHs) carrying CQIsrepresenting status information about downlink radio channels.
 16. Themethod of claim 13, wherein an ACK/NACK for a first data channel amongnon-persistently scheduled data channels is transmitted in ACK/NACKresources implicitly mapped to an SCCH corresponding to the first datachannel in the first resource group, the first channel carrying a firstcodeword among a plurality of codewords for Multi-CodeWord-MultipleInput Multiple Output (MCW-MIMO), and ACK/NACKs for second data channelscarrying remaining codewords are transmitted in explicitly signaledACK/NACK resources in the second resource group.
 17. The method of claim13, wherein an ACKCH corresponding to the non-persistently scheduleddata channel has a relatively long first transmission duration, and theACKCH corresponding to the persistently scheduled data channel has oneof the first transmission duration and a relatively short secondtransmission duration.
 18. The method of claim 13, wherein remainingresources that are not allocated as ACK/NACK resources for thenon-persistently scheduled data channel are allocated for transmissionof at least one ACKCH for persistently scheduled data channels, CQICHs,and predetermined other channels and explicitly signaled.
 19. Anapparatus of a User Equipment (UE) for receiving ACKnowledgment/NegativeACKnowledgment (ACK/NACK) resources in a wireless communication system,comprising: a controller for determining to use ACK/NACK resourceswithin a predetermined fixed-size first resource group for ACK/NACKtransmission for a non-persistently scheduled data channel, the ACK/NACKresources being implicitly mapped to a Scheduling Control CHannel (SCCH)carrying scheduling information about the non-persistently scheduleddata channel, if the non-persistently scheduled data channel isallocated to the UE, and determining to receive resource indicationinformation explicitly indicating allocated ACK/NACK resources for anACK/NACK CHannel (ACKCH) corresponding to a persistently scheduled datachannel within a predetermined flexible-size second resource group, ifthe persistently scheduled data channel is allocated to the UE; and areceiver for receiving the resource indication information under controlof the controller.
 20. The apparatus of claim 19, wherein an ACK/NACKfor initial transmission data on the persistently scheduled data channelis transmitted in the ACK/NACK resources explicitly indicated by theresource indication information, and an ACK/NACK for retransmission dataassociated with the initial transmission data is transmitted in ACK/NACKresources implicitly mapped to an SCCH carrying scheduling informationabout the persistently scheduled data channel.
 21. The apparatus ofclaim 19, wherein the second resource group is shared between ACKCHs forpersistently scheduled data channels and Channel Quality IndicatorCHannels (CQICHs) carrying CQIs representing status information aboutdownlink radio channels.
 22. The apparatus of claim 19, wherein anACK/NACK for a first data channel among non-persistently scheduled datachannels is transmitted in ACK/NACK resources implicitly mapped to anSCCH corresponding to the first data channel in the first resourcegroup, the first channel carrying a first codeword among a plurality ofcodewords for Multi-CodeWord-Multiple Input Multiple Output (MCW-MIMO),and ACK/NACKs for second data channels carrying remaining codewords aretransmitted in explicitly signaled ACK/NACK resources in the secondresource group.
 23. The apparatus of claim 19, wherein an ACKCHcorresponding to the non-persistently scheduled data channel has arelatively long first transmission duration, and the ACKCH correspondingto the persistently scheduled data channel has one of the firsttransmission duration and a relatively short second transmissionduration.
 24. The apparatus of claim 19, wherein remaining resourcesthat are not allocated as ACK/NACK resources for the non-persistentlyscheduled data channel are allocated for transmission of at least oneACKCH for persistently scheduled data channels, CQICHs, andpredetermined other channels and explicitly signaled.